1. Technical Field of the Invention
The present invention relates generally to an angular rate sensor which may be employed in an attitude control system for automotive vehicles, a hand-sake compensating system for video cameras, or a gyroscope of a navigation system for moving objects. Particularly, the invention relates to an improved structure of an angular rate sensor for minimizing output noise which includes a drive tuning fork functioning as a self-excited oscillator and a measuring tuning fork serving to measure the angular rate of motion applied to a moving object.
2. Background Art
Japanese Patent First Publication No. 8-2278141, which corresponds to European Patent Application No. EP764828, teaches an angular rate sensor which has four tines of which two outer tines serve as a drive tuning fork and the other inner tines serve as a measuring tuning fork. The four tines are connected at ends thereof through a support member and extend in parallel to each other to have a comb-like configuration.
In operation, the tines of the drive tuning fork are electrically excited to vibrate in opposite directions. When the angular motion is applied to the sensor during the electrically energized vibrations of the drive tuning fork, the energy to vibrate the drive tuning fork in a direction perpendicular to the electrically excited vibrations is transmitted to the measuring tuning fork through the support member to vibrate the tines of the measuring tuning fork, which vibration is outputted as a signal indicative of the angular rate of the motion of the sensor. The tines of the sensor are, as described above, grouped into the drive tuning fork and the measuring tuning fork, which will result in an S/N (signal-to-noise) ratio higher than that of a two-tine sensor, but the inventors of this application studied the above prior art and found the disadvantage that a desired S/N ratio is not obtained for the following reasons.
The drive tuning fork and the measuring tuning fork are, as described above, connected at ends thereof through the support member, thus causing the energy of self-excited oscillation of the drive tuning fork to leak to the measuring tuning fork, which will contribute to undesired vibrations of the measuring tuning fork even when no angular motion is applied to the sensor, thereby developing electrical noise undesirably.
Further, enhancing the sensitivity of the sensor requires effective transmission of vibratory energy to the measuring tuning fork which is produced by the Coriolis force resulting from application of angular motion to the sensor, but the above prior art structure dampens the vibration transmitted to the measuring tuning fork greatly, thus resulting in a decrease in sensitivity of the sensor.